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In case you do not receive Zalo’s ringtone when in locked mode, please follow Taimienphi’s instructions below to be able to receive Zalo calls on Lumia normally:

– Zalo for Windows Phone: Download Zalo for Windows Phone Lumia, Microsoft Lumia

Step 1 : You go to Settings (Settings)

Step 2: Scroll down and find the item save energy

Step 3 : Swipe left, right to go to the usage window, find the Zalo application and click to select.

Step 4 : Section “Allow apps to run in the background” you switch from Off to On.

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So, the fact that Zalo or other applications do not have notifications when locking the device is because you have not allowed the application to run in the background, but activating it in the background will mean more battery consumption.